Shift to litterfall as year-round forage for sika deer after a population crash

Abstract

We determined that litterfall was utilized as the main food throughout the year after the first crash of a sika deer population in 1984 on Nakanoshima Island, Toya Lake, Hokkaido, Japan. Palatable plants and leaves of broad-leaved trees decreased to 0.1% of biomass within the browse category in 1994. Meanwhile, unpalatable plants such as senecio (Senecio cannabifolius), chloranthus (Chloranthus japonicus), and spurge (Pachysandra terminalis) occupied 99.9% of biomass on the forest floor. Species richness of the forest floor plants declined greatly. Litterfall is a stable and abundant resource although its consumption requires more time than browsing on leaves of trees if they are available. We propose that a shift to litterfall as alternative food will continue to support a relatively high density sika deer population. However, the high deer population will come at the cost of few palatable plants and tree seedlings within the browsing reach of deer, dominance of unpalatable plants, and a decline of plant species richness for a long time in the post-peak stage.